When HPD officer Ben Keoki is shot by a sniper in broad daylight, Five-0 joins the case to hunt for the mystery killer. A specialized bullet casing is found near the sniper's nest with the victim's name engraved on it, leading McGarrett to posit that this is just the first of many killings by the gunman. Later, an anonymous tip draws HPD and Five-0 to a home where a drug dealer is holed up and engaging in a firefight with the police. During the firefight, another officer, Troy Ookala, is gunned down, hit by the same sniper. It becomes clear that the sniper is targeting police officers, so Five-0 works to figure out what Ookala and Keoki had in common. Things take a dark turn when McGarrett narrowly misses getting shot by the sniper himself, and then Sgt. Lukela gets shot as well. McGarrett and Danny manage to chase the sniper and force his car into the ocean, but he gets away before they can arrest him. They recover a prosthetic hand at the scene, which allows McGarrett to put the puzzle pieces together. McGarrett's father, Lukela, Keoki, and Ookala were all awarded medals for stopping an armed bank robbery years ago, and the perpetrator of that robbery had his hands blown off by his own explosives in the gunfight at the bank. That man, Curt Stoner, (the 'Hookman') was given two prosthetic hands in prison, and he vowed to get revenge on the men who put him there. Five-0 manages to lure Stoner out, using McGarrett as live bait, and Kono takes him out with a perfect shot of her own.